Pressure regulator

ABSTRACT

A large vacuum pump is connected through a vacuum line to the cow milking apparatus, and a vacuum regulator is employed to admit into the line the amount of ambient air necessary to maintain the line pressure (and thus the pressure at the milking apparatus) constant within very narrow limits. The vacuum regulator comprises an air valve to control the admission of ambient air, and which is itself controlled by a light bias spring (having a low spring rate) and an opposed diaphragm. One side of the diaphragm is subjected to pressure generally equal to line pressure, whereas the other side of the diaphragm is subjected to pressure of air within a stabilizing and regulating dome. Adjustable means responsive to the pressure differential between the dome and ambient are provided to admit into the dome sufficient air to maintain the dome pressure constant. Furthermore, means are provided to bleed air through the diaphragm, thus maintaining substantially constant the pressure drop thereacross. The air valve is constructed with large radial ports which admit air radially over the thin edge of a slide valve, and in response to only a small valve movement. The very stable and controlled dome pressure, the substantially constant pressure drop across the diaphragm, the light bias spring, and the described air valve construction cooperate to result in extreme sensitivity and low-inertia operation and thus in very close regulation of line pressure.

This is a division of application Ser. No. 336,186, filed Feb. 27, 1973,now U.S. Pat. No. 3,811,467.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of milking machine systems.

2. Description of Prior Art

The regulation of vacuum in cow milking machine systems is, at present,generally poor. Thus, for example, when air is drawn into the vacuumline through one or more sets of teat cups, the pressure increase(vacuum decrease) in the system may be so great that the teat cups fallfrom the udders of large numbers of cattle. Conversely, the pressure mayat times be so low (vacuum so high) that the teats are injured. Thereexists a major need for a milking machine system capable of milkinglarge numbers of cows, and wherein the pressure (vacuum) stayssubstantially constant, at all times, regardless of such factors as thedrawing-in of air through the teat cups for one, or a number of, cows.

The vacuum regulators in prior-art milking systems were normallyhigh-inertia devices which sensed the pressure at regions of high airvelocity--which velocity created localized pressure changes and thusresulted in errors. Because of the high inertia, changes in linepressure could not be compensated for with sufficient rapidity.Prior-art regulators in milking systems were also characterized by thepresence of air valves which were affected by air flow velocity andwhich could not pass volumes of air adequate to compensate rapidly forsudden changes in line pressure. Such regulators required major axialmovement of the air valves, with consequent excessive changes in theforces exerted by the biasing springs. Furthermore, such biasing springswere often undesirably large and heavy. These, and other, factorsresulted in the unsatisfactory pressure regulation outlined in thepreceding paragraph.

There exist large numbers of vacuum regulators in arts not related tomilking machine systems. Such regulators are, insofar as applicant isaware, unsatisfactory in the milking machine art. There are numerousreasons for this, including one or more of the following: (a) Suchvacuum regulators are not adapted to handle the high-flow and dynamicconditions present in large milking systems. (b) Such regulators were ofthe "series" type, which would, if incorporated in a vacuum line to amilking machine, create major problems relative to cleaning of theregulator and relative to danger of damage to the vacuum pump. (c) Suchregulators were of complex, and thus expensive, construction.

Summary of the Invention

In the present milking machine system, the pressure (and vacuum)regulator is not in series with the vacuum line, being instead adaptedto admit the amount of ambient air necessary to maintain the desiredline pressure. The regulator incorporates an air valve which is operatedby a diaphragm and by an opposed light bias spring. To determine the setpoint of the system, one side of the diaphragm is exposed to the airwithin a dome. The dome is supplied with air from the ambientatmosphere, through a pressure-determining inlet valve which isadjustable to cause the dome pressure to remain constant at any desiredlevel. Air from the dome is bled through the diaphragm, thus causing thepressure drop thereacross to be substantially constant. The other sideof the diaphragm is exposed to a sensing chamber, into which the air isbled. Such chamber communicates selectively with a plurality of regionsof the milking machine system, which regions are characterized byrelatively low air velocity.

The air valve has a plurality of low-inertia wheels which move axiallyin conjoint manner, in sliding contact with the wall of the valvechamber. Such wall incorporates many large radial air ports which, whennot blocked by the wheels, admit air from the ambient atmosphere. Theports associated with one wheel are offset relative to those associatedwith the other, so that simultaneous unblocking of both sets of ports isprevented. The wheel regions over which air flows when entering theports have very thin radial dimensions, thus reducing to a minimum theeffects of air velocity on valve operation.

The pressure-determining inlet valve to the dome is of an improvedconstruction which maximizes control of pressure while improving shelflife.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of the present milking machine system, themilking machine and vacuum pump being shown schematically;

FIG. 2 is an enlarged vertical sectional view of the pressure-regulatingportion of the milking machine system, portions of the dome being brokenaway;

FIG. 3 is a horizontal sectional view taken on line 3--3 of FIG. 2;

FIG. 4 is a vertical sectional view corresponding to the central regionof FIG. 2, but showing the air valve in an open position;

FIG. 5 is a greatly enlarged view showing one region of the showing ofFIG. 4, the air valve being less open;

FIG. 6 is an enlarged view showing a check valve which bleeds air fromthe dome through the diaphragm to the sensing chamber; and

FIGS. 7 and 7a are enlarged vertical sectional views showing twoembodiments of the air-inlet and regulating valve to the dome.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Throughout this specification and claims, to minimize confusion,reference is normally made to "pressure" instead of "vacuum", eventhough the "pressure" is less than atmospheric. Thus, the pressuresreferred to in the specification are absolute pressures as distinguishedfrom gauge pressures, namely psia as distinguished from psig.

Referring first to FIG. 1, a cow milking machine system is illustratedto comprise a milking machine 10 which is connected by a vacuum line 11to a vacuum pump 12. The milking machine may incorporate large numbersof teat cups as well as milk traps, valves, etc. The vacuum line 11 maybe very long and may also incorporate valves, bends, etc. The vacuumpump 12 is often a high power high-volume pump which exhausts air fromthe line 11 to the atmosphere. A typical pump for a large system has onthe order of 5-35 horsepower and is able to pass 100-300 cubic feet perminute of air. The milking machine system may be adapted to milk largenumbers (for example, 30) of cows simultaneously.

Vacuum pump 12 is so operated that it will always attempt to draw online 11 a greater vacuum than that which is desired to be present in theline. Therefore, to control the line pressure, ambient air is introducedinto the line in the proper amount to cause the line pressure to be setat a fixed value which is regulated within narrow limits by the presentinvention. This value is, because of the introduction of ambient air,higher than that which the vacuum pump 12 is attempting to achieve. Theambient air is introduced by a pressure (and vacuum) regulator 13 whichis described in detail below.

Pressure regulator 13 comprises a cup-shaped body 14 over which issecured, by screws 15, a diaphragm-mounting ring 16. A large dome 17 issealingly mounted on ring 16, as by welding, and has incorporated in theupper portion thereof an air-inlet and pressure-controlling valve 18. Adiaphragm 20 is mounted across the lower end of the dome, having itsedge portion sealingly mounted between mounting ring 16 and the rim ofbody 14.

The peripheral region of diaphragm 20 is not confined in any way exceptat the extreme edge, so that friction is minimized. The remainingregions of the diaphragm are confined between diaphragm plates 21 whichcomprise lightweight metal members. The dome 17, diaphragm 20 and ring16 define a large "dome chamber" 22 which is highly important to thepresent pressure regulator.

An air valve 24 is mounted below body 14, and comprises a cylindricalbody 25 having a diameter substantially less than that of body 14. Theupper end of body 25 is secured by screws 26 to the body 14, whereas thelower end of body 25 is suitably and sealingly connected by couplingmeans 26a to a Tee 27 (FIG. 1) in vacuum line 11. If desired, a checkvalve (not shown) may be incorporated below air valve 24, for example inTee 27, to insure against upward movement into the regulator 13 of waterwhich is used for washing the milking machine and vacuum pump. Suchcheck valve only permits downflow of air from the regulator 13 to thevacuum line, without permitting major amounts of reverse flow.

An annular groove or recess 28 is provided on the exterior ofcylindrical body 25. Mounted around the body 25, and encompassing groove26, is an annular air filter 29 having end rings 30. A mounting ring 31is threadedly associated with body 25, beneath groove 28, and bearsagainst the lower end ring 30 to thereby force the upper end ringagainst the underside of the cup-shaped body 14. Thus, all air whichpasses to the region of annular groove 28 is filtered.

Two rows 32 and 33 of radial air ports 34 are provided at longitudinallyspaced regions along the valve body 25. Each port row 32 and 33 extendscircumferentially of the body 25, and lies generally in a planeperpendicular to the axis of such body. As shown in FIG. 3, the radialports 34 in each row are not circular but instead are circumferentiallyelongated slots having large cross-sectional flow areas.

First and second "wheels" 36 and 37 are mounted within body 25 andrespectively adjacent the port rows 32 and 33, lying in spaced parallelplanes which are perpendicular to the axis of valve body 25. The wheelsare so designated because of their shapes; they do not rotate. Each is arelatively lightweight metal element having spokes 38 (FIG. 3), a hub 39and an axially-elongated rim 41. The exterior surface of each rim 41 iscylindrical and is in sliding contact with the cylindrical interiorsurface of valve body 25. The spokes 38 define between them large-areaair openings 42 (FIG. 3) through which air may flow into the vacuum line11 after entering through radial ports 34.

The hubs 39 of the first and second wheels 36 and 37 are axiallyelongated and are fixedly secured, as by brazing or welding, to theexterior surface of an axial stem 43 which is mounted at the axis ofvalve body 25. One portion of stem 43 extends slidably through a centralopening in the bottom wall of body 14. The lower end of the stem extendsslidably through a wheel-shaped stem guide 44, the latter having acentral hub, radial spokes and a peripheral rim which is locked by asnap ring 46 to body 25.

The upper end of stem 43 extends through central openings in diaphragmplates 21 and in diaphragm 20. A retaining cap 47 is mounted over theupper stem end, and seats on the upper diaphragm plate 21 so as to forcethe lower diaphragm plate against a shoulder on the stem. Thus, when ascrew 48 is threaded downwardly through the cap and into the stem, theupper stem end is locked to the diaphragm assembly.

When the pressure in dome chamber 22 exceeds that in the chamber beneaththe diaphragm assembly (which chamber is numbered 49 and may be termedthe "sensing chamber"), the diaphragm assembly and the stem are forceddownwardly and move the valve wheel rims 41 sufficiently far that air isadmitted through ports 34. An axially-mounted helical compression spring51 is supported at its lower end on stem guide 44 and is seated at itsupper end on the under portion of the lower valve wheel 37. Thus, spring51 is a biasing spring which opposes the diaphragm and tends to causeclosing of the air valve.

Spring 51 is relatively light and has a low spring rate; therefore, thebias exerted by the spring does not change to a considerable extent inresponse to the relatively small axial shifting of the valve wheels 36and 37. Spring 51 is somewhat preloaded, for example to about 14 poundsin a valve wherein the diameter of the diaphragm 20 is about 6 inchesand the diameter of each valve wheel 36 and 37 is about 3-1/2 inches.

Although it is very important that the operation of the present vacuumregulator be fast, the amount of friction should not be so low thatthere is excessive overtravel of the valve elements, with resultantpossibility of instability. To prevent such operation, a damping means52 is mounted around the lower end of stem 43. The damping means 52comprises a Teflon ring 53 which is split at one point about itscircumference, and has mounted therearound in an external groove thereina helical tension spring 54, the latter tending to squeeze the ringaround the stem to thus introduce friction between the inner cylindricalsurface of ring 53 and external cylindrical surface of the stem. Theamount of such squeezing, and thus the amount of friction increase, isdetermined by the tension of the spring 54. The ring 53 is preventedfrom moving, since the lower portion thereof is seated on stem guide 44and the upper portion thereof is held down by spring 51.

To additionally prevent valve instability, etc., the degree of registryof the upper valve wheel 36 with its associated row 32 of ports 34 iscaused to be different from the degree of registry of the lower valvewheel 37 with its associated port row 33. Referring particularly to FIG.5, it will be noted that the upper valve wheel 36 is still blocking itsassociated ports 34, at the same time that the lower valve wheel 37 haspartially opened relative to its associated port row. Thus, all of theintroduction of air is (when the valve is in the FIG. 5 position)through the lower port row 33. When further air introduction isrequired, the valve wheel assembly will move down an additional amountso that air will be admitted simultaneously through both rows 32 and 33of ports 34, as shown in FIG. 4.

It will thus be seen that the present air valve assembly is capable ofadmitting large amounts of air in response to only small axial shiftingof the wheels 36 and 37, which small axial shifting does not changesubstantially the bias force exerted by spring 51. However, therelationship is such that only the required amount of air is admitted,and tendencies toward instability are minimized. If desired, additionalwheels and associated port rows may be provided above or below thoseshown in the drawings.

It is important to minimize the tendency of the inrushing air (throughports 34) to affect the positions of valve wheels 36 and 37, since suchpositions should be determined solely by the spring 51 and by thediaphragm assembly. Because the air flow through ports 34 is radial, andbecause the air openings 42 are very large and the spokes 38 are small(FIG. 3), there are little or no direct pressure affects exerted by theair relative to the wheels 36 and 37. However, the air which passesradially-inwardly over the upper edges of rims 41 does tend to createlow pressure regions and to "suck" the rims upwardly. To minimize thiseffect, the upper edge regions of the rims are beveled so that theextreme upper edges are very small in radial dimension. Because of suchbeveling, the upward (sucking) force exerted when the air flows radiallyinwardly through ports 34 is minimized.

It is also important that the movements of the diaphragm do not altersubstantially the pressure present in dome chamber 22. Therefore, thedome is caused to be sufficiently large that the diaphragm movementswill effect only a small percentage change in dome volume, and thus onlya slight change in dome pressure. The number of cubic inches in domechamber 22 should be at least several times the number of square inchesin the area of the diaphragm. In the illustrated embodiment, this factoris about 6 (cubic inch dome volume about 6 times the square inchdiaphragm area).

Proceeding next to a description of the air-inlet andpressure-controlling valve or regulator 18, this is best shown in FIG.7, and comprises means to maintain substantially constant the airpressure in dome chamber 22. Furthermore, the constant pressure inchamber 22 is maintained a predetermined constant pressure differentialbelow the pressure of the ambient atmosphere.

Valve 18 comprises a body 56 which is extended downwardly through anopening in dome 17, and is externally threaded at the lower portionthereof to receive an internally threaded conduit 57. At the lower endof conduit 57 is mounted a bellows-supporting ring 58 to which is sealedthe lower end of a bellows 59 having a horizontal plate 60 at the upperend thereof. The bellows 59 acts as a spring to bias the plate 60upwardly.

The extent of upward movement of bellows plate 60 is determined by anadjustable screw 61 which is threaded downwardly through adownwardly-protuberant central boss portion 62 of valve body 56. Thelower end of screw 61 has a frustoconical surface 63 and adownwardly-extending cylindrical bellows guide portion 64 which extendinto a central opening 66 in the bellows plate.

A chamber 67 is defined below valve body 56, within conduit 57 and abovethe bellows 59. The only way for air to enter such chamber 67 is throughpassages 68 in the valve body, the upper ends of such passagescommunicating through air filters 69 with the ambient atmosphere. Thefilters 69 are secured in place by suitable snap rings or other securingmeans, numbered 70.

When the set screw 61 is threaded upwardly to such position that thespring force exerted by bellows 59 is barely sufficient to seat plate 60on surface 63, then the bellows will tend to open when the pressure indome chamber 22 is only a small amount below atmospheric pressure. Onthe other hand, when set screw 61 is threaded downwardly to compress thebellows 59 to a considerable degree, then then the pressure in domechamber 22 must reduce by a major amount (below that of the ambientatmosphere) before the plate 60 will be shifted off of seat 63 so thatair may be introduced through opening 66 and into dome chamber 22.

The air in dome chamber 22 is not static, since there is a slow butsubstantially continuous flow therethrough from the ambient atmospherethrough opening 66 to the chamber 22, and from the chamber 22 into thesensing chamber 49. The latter flow is through a small-diameter bleedport 72 (FIG. 6) in the diaphragm assembly 20-21. A flap valve 73 in theform of a rubber element having a very small bias is provided at thelower surface of the diaphragm assembly over the port 72, and serves topermit downward bleeding of air from chamber 22 to chamber 49 but toprevent substantial upward passage of air or water. The valve 73performs the function of insuring that any wash water which is passedthrough the line 72 in order to clean the same of milk does not find itsway upwardly into the dome 22.

After the air has bled through port 72 into the sensing chamber 49, itis passed through one of two alternately-employed sensing means. Thefirst may be termed the "direct sensing means" and comprises ports 75(FIG. 2) in stem 43 and which pass air from sensing chamber 49 to anaxial passage 76 in the stem. The lower end of passage 76, when plug 81is removed, communicates with the Tee 27 associated with line 11 (FIG.1), so that the lower end of the passage 76 is responsive to thepressure in the Tee and thus in the line 11.

In some large systems the line 11 is long and may incorporate variousvalves, bends, etc., causing the pressure at the milking machine 10 tobe substantially different from that at the regulator 13. In suchsystems, it is often desirable to employ a "remote sensing means"comprising a conduit 77 which communicates with a port 78 in body 14 andthus with the sensing chamber 49. The conduit 77 extends to any suitablepoint in line 11, for example to a region adjacent the milking machine10 as shown in FIG. 1.

When direct sensing is desired, a valve 79 in conduit 77 (FIG. 1) iscaused to be shut, and the axial passage 76 in stem 43 is open andcommunicates with the Tee 27. Conversely, when remote sensing isdesired, valve 79 is opened and a plug 81 (FIG. 2) is mounted in thelower end of stem 43 and secured in position as by a cotter pin.

The port 72 through the diaphragm assembly is caused to be sufficientlylarge that it will not tend to become clogged by dust, etc., and to besufficiently small that a pressure differential may exist between thepressure in dome chamber 22 and the pressure in sensing chamber 49. Inthe exemplary valve wherein the diameter of diaphragm assembly is about6 inches and that of the valve wheels 36 and 37 about 3-1/2 inches, thediameter of port 72 may be (for example) 0.040 inch.

The diameter of the central opening or port 66 in bellows plate 60 mustbe sufficiently large to satisfy air flow through port 72 in thediaphragm assembly. Thus, sufficient air may be admitted through port 66to permit the diaphragm assembly to move upwardly and downwardly underthe influence of the pressure in sensing chamber 49 (relative to that inthe dome chamber) and under the influence of spring 51. In the presentexample, the diameter of port 66 may be 0.067 inch.

OPERATION

Let it be assumed that the system as shown in FIG. 1, that the vacuumpump 12 is not in operation, and that everything is initially atatmospheric pressure (about 15 psia).

In the previously-stated example, wherein the preload of spring 51 is 14pounds, and the diameter of diaphragm 20 is 6 inches, the area of thediaphragm is approximately 28 inches. Because of these relationships, apressure differential across the diaphragm assembly of a little morethan 1/2 psi causes the diaphragm to shift downwardly and initiateopening of the air valve.

As soon as vacuum pump 12 is started in operation, the reduced linepressure is transmitted through the operative one of sensing conduits 76or 77 to the sensing chamber 49, and quickly causes the pressuredifferential across the diaphragm to be above 1/2 psi. The diaphragm isthen sucked downwardly and effects partial opening of the air valve, sothat air is drawn in through various ports 34 and through the Tee 27into the vacuum line.

As the line pressure continues to decrease, the pressure in sensingchamber 49 decreases, and this decrease is reflected (due to flowthrough port 72) by a corresponding decrease in the pressure in domechamber 22. Thus, for example, the pressure in the dome chamber alwaysremains about 1/2 psi above the pressure in sensing chamber 49.

It follows that the pressures will decrease until the "set point" ofValve 18 (FIG. 7) is reached, which may (for example) occur when thedome pressure is 9 psia. Reaching of such set point causes the bellowsplate 60 to move downwardly off seat 63 and thereby admit air into thedome through port 66. This initiates a "floating" operation of thebellows plate relative to seat 63, whereby sufficient air is admitted tocause the dome pressure to remain substantially constant at (forexample) 9 psia.

Although the dome pressure is now 6 psi less than atmospheric, thepressure drop across the diaphragm has remained substantially constantat (for example) 1/2 psi. Thus, the downward pressure exerted by thediaphragm on stem 43, and on the valve wheels 36 and 37, remainsconstant and balances the upward pressure exerted by bias spring 51.This balanced relationship results in the inflow of the proper amount ofair through various ports 34 to cause the pressure line 11 to remainsubstantially constant.

Let it be assumed, for example, that the line pressure reduces slightlyfrom the desired substantially constant value. The reduction in linepressure is transmitted through the operative one of conduits 76-77 tosensing chamber 49, which decreases the pressure in chamber 49 andpermits the diaphragm assembly to move downwardly and open valve wheels36 and 37 to a greater extent relative to the associated ports 34.Additional air is therefore drawn in through ports 34 to the line, tocompensate for the decrease in pressure.

Conversely, let it be assumed that the line pressure increasesmomentarily relative to the desired substantially constant valve. Theincrease is transmitted through one of the conduits 76-77 to sensingchamber 49, and causes upward movement of the diaphragm (which upwardmovement is aided by the bias spring 51). The valve wheels 36-37 arethen closed to an additional extent relative to their associated ports34, thus reducing the inflow of air through the air valve means andcausing a lowering of the line pressure.

As previously noted, if the change in line pressure is small, only thelower one (37) of the valve wheels is operated to open the associatedports 34 in the lower port row 33, since the upper wheel 36 remains inblocking relationship to its associated port row 32. However, arelatively extreme change in line pressure will cause both rows of portsto be at least partially unblocked, to thereby rapidly compensate forthe pressure change.

It is pointed out that there is a large air flow through the line, and alarge and rapid air flow through the ports in one or both rows 32-33.Furthermore, there is a substantially continuous flow of air through thediaphragm port 72 and also through port 66 in the bellows plate. The airflow through the port 66 is modulated by vibratory upward and downwardmovement of the plate 60 which creates a modulating and regulatingaction to maintain the dome pressure constant within very close limits(such as, for example, 0.05 psi). This very constant dome pressurecreates a substantially constant pressure in the line 11, despitevarious factors (such as drawing in of air through one or more sets ofteat cups, and such as variations in the operation of the pump 12,etc.). With the described system, the line pressure may be maintainedconstant within about 0.1 psi, for example.

The constant line pressure is highly important in creating the correctamount of suction for milking purposes, and preventing injury to theteats of the cows' udders, and preventing dropping of the teat cups offall of the cows being milked despite large amounts of air inflow throughsets of teat cups, etc.

It is to be noted that the degree of movement of stem 43 and of thevalve wheels 36 and 37 is very small, for example, less than 0.050 inchper 100 cfm (cubic feet per minute) flow change, this being possiblebecause of the large port area which can be uncovered in response tosuch small movement. It follows that the change in the spring rate ofspring 51 is extremely small, which small change (when coupled with theconstant pressure drop across the diaphragm assembly) causes very closeregulation of the pressures. It also follows that the diaphragm movementis small, and this when coupled with the large dome volume assures asubstantially constant dome pressure.

When it is desired to change the line pressure, it is merely necessaryto turn the set screw 61 (FIG. 7). This is accomplished very easily.There is thus readily achieved a new set point in dome pressure, whichresults in a new set point in the line pressure.

EMBODIMENT OF FIG. 7a

The embodiment of FIG. 7a is identical to the embodiment previouslydescribed, except for the construction of the portion ofpressure-regulating valve 18 which is adjacent bellows plate 60.

Referring to FIG. 7a, the lower end of adjustable screw 61a does nothave the portions 63 and 64 of the previous embodiment, being insteadprovided with a radial flange 90 which has a depending peripheral skirt91. A soft ring 92, formed of a soft elastomeric material, is bonded tothe upper surface of bellows plate 60 in encompassing relationship toopening 66. The upper-central portion of the ring is caused to beprotuberant in order to form a Seat 93 for the lower (radial) surface ofscrew 61a.

The vertical dimension of skirt 91 is caused to be slightly less thanthe vertical dimension of ring 92 (including seat 93). Therefore, seat93 engages the screw end prior to the time that the lower edge of theskirt is engaged by plate 60. When the skirt 91 is engaged by plate 60,for example when the system is not in operation, the skirt preventexcessive compression and "setting" of the elastomeric part 92-93. Thus,the "shell life" of the present valve is improved.

The valve of FIG. 7a is believed to operate better than that of FIG. 7,particularly in locations where there is not much vibration. The valveof FIG. 7a achieves an extremely close and reliable regulation of domeair pressure.

The foregoing detailed description is to be clearly understood as givenby way of illustration and example only, the spirit and scope of thisinvention being limited solely by the appended claims.

I claim:
 1. A pressure regulator for Tee connection to the line whichextends between the vacuum pump and the milking machine of a cow milkingmachine system, said pressure regulator comprising:a. air valve means toadmit atmospheric air into said line, b. a diaphragm connected to saidair valve means, c. spring means connected to said air valve means andbiasing the same toward closed condition, d. means to define a domechamber on one side of said diaphragm,said one side of said diaphragmbeing such that an increase in the air pressure in said dome chamberrelative to the air pressure on the other side of said diaphragm causessaid disphragm to oppose said spring means and to open said air valvemeans, and a decrease in the air pressure in said dome chamber relativeto the air pressure on said other side of said diaphragm causes saiddiaphragm to aid said spring means in closing said air valve means, e.means to admit atmospheric air into said dome chamber and to maintainthe air pressure in said dome chamber at a predetermined constant valuesubstantially below atmospheric pressure, f. means to bleed air fromsaid dome chamber to said line, and g. means to subject said other sideof said diaphragm to the air pressure of said line,whereby said airvalve means is caused to admit into said line sufficient atmospheric airthat the pressure in said line remains substantially constant.
 2. Theinvention as claimed in claim 1, in which said means recited in clause(f) comprises means to maintain the air pressure on said other side ofsaid diaphragm at a substantially constant differential below the airpressure in said dome chamber.
 3. The invention as claimed in claim 1,in which said means recited in clause (f) comprises means to bleed airfrom said dome chamber to said other side of said diaphragm.
 4. Theinvention as claimed in claim 3, in which said bleed means comprises asmall opening in said diaphragm, and in which a check valve is providedto minimize flow of fluid through said small opening in a directiontoward said dome chamber.
 5. The invention as claimed in claim 1, inwhich means are provided to define a sensing chamber one wall of whichis said other side of said diaphragm, and in which said means recited inclause (g) effects selective connection between said sensing chamber andthe region of said line adjacent said air valve means, and between saidsensing chamber and a region of said line remote from said air valvemeans.
 6. The invention as claimed in claim 1, in which the volume ofsaid dome chamber is large in comparison to the diameter of saiddiaphragm.
 7. The invention as claimed in claim 1, in which said biasspring has a low spring rate, and in which said air valve means movesonly a small distance in shifting between said one position and saidopposite position.
 8. The invention as claimed in claim 1, in which saidair valve means comprises a cylindrical conduit connected to said linein Tee relationship, a valve wheel mounted coaxially in said conduit andhaving a cylindrical rim portion in axially slidable engagement with theinterior cylindrical surface of said conduit, and a set of radial portsprovided through the wall of said conduit, said ports being adapted tobe blocked by said rim when said valve wheel is in one axial position insaid conduit, and to be unblocked when said valve wheel is in anotheraxial position in said conduit.
 9. The invention as claimed in claim 8,in which the edge of said wheel rim, over which air passes in enteringthrough said ports, has a small radial dimension, thereby minimizing thesuction effect created by air flow through said ports.
 10. The inventionas claimed in claim 8, in which a second and corresponding valve wheeland an associated set of radial ports provided in said air valve means,said second valve wheel having an axial position to its set of portswhich is somewhat different from the axial position of saidfirst-mentioned valve wheel relative to its set of ports.
 11. Theinvention as claimed in claim 1, in which adjustable means are providedto create a predetermined amount of friction in said air valve means.12. The invention as claimed in claim 1, in which said means recited inclause (e) comprises a flexible resilient element one side of which isexposed to atmospheric pressure and the other side of which is exposedto the pressure in said dome chamber, a portion of said element havingan opening therein to admit atmospheric air into said dome chamber, inwhich an adjustable element is mounted opposite said opening, and inwhich a soft annular seat is provided coaxially of said opening andinterposed between said adjustable element and said portion, said seatpreventing air flow through said opening when said portion is near saidadjustable element, said seat permitting air flow through said openingwhen said portion is relatively remote from said adjustable element. 13.The invention as claimed in claim 12, in which said seat is sealinglysecured to said portion of said flexible resilient element.
 14. Theinvention as claimed in claim 12, in which said flexible resilientelement is a bellows.
 15. The invention as claimed in claim 12, in whichstop means are provided to determine the maximum degree of compressionof said soft seat.
 16. The invention as claimed in claim 15, in whichsaid adjustable element is a screw having a flange at the end thereof,and in which said stop means is a skirt on said flange and adapted to beengaged by said portion of said flexible resilient element.
 17. Apressure regulator for Tee connection in the line which extends betweenthe vacuum pump and the milking machine of a cow milking machine systm,said pressure regulator comprising:a. a conduit connected to said linein Tee relationship, b. air valve means to admit atmospheric air intosaid conduit, c. spring means connected to said air valve means to urgethe same toward closed position preventing admission of atmospheric airinto said conduit, d. a diaphragm connected to said air valve means, e.wall means provided on the side of said diaphragm rmote from saidconduit,said wall means defining a dome chamber, f. means to admitatmospheric air into said dome chamber and to maintain the pressure insaid dome chamber at a predetermined substantially constant level belowthat of the ambient atmosphere, g. means to effect communication betweensaid line and the side of said diaphragm adjacent said conduit, and h.means to effect bleeding of air from said dome chamber to said adjacnetside of said diaphragm and to maintain the air pressure on said adjacentside of said diaphragm at a predetermined substantially constantpressure differential below that in said dome chamber,whereby thepressure in said line is caused to be substantially constant level at alevel which is related to the pressure in said dome chamber.
 18. Theinvention as claimed in claim 17, in which said spring means is arelatively lightweight spring having a low spring rate, in which saiddiaphragm is a large-area diaphragm, and in which said diaphragm andsaid spring substantially counterbalance each other when there is only arelatively small pressure drop across said diaphragm.
 19. The inventionas claimed in claim 17, in which said means recited in clause (f)comprises a bellows having a bellows plate at one end thereof, saidbellows plate having an opening therein, one side of said bellowscommunicating with the ambient atmosphere, the other side of saidbellows communicating with said dome chamber, said opening in saidbellows plate introducing air from the ambient atmosphere into said domechamber, and in which the spring force of said bellows tends to seatsaid plate on an adjustable screw having a tapered seat portion whichpartially penetrates said opening in said bellows plate.
 20. Theinvention as claimed in claim 17, in which said conduit has acircumferential row of radial air ports therethrough, and in which saidair valve means comprises a lightweight valve wheel the rim of which hasa cylindrical exterior surface in sliding contact with the interiorcylindrical wall of said conduit adjacent said air ports.
 21. Theinvention as claimed in claim 20, in which the edge of said rim overwhich air passes when entering said ports has a small radial dimension.